The term “position regulation” as used herein encompasses a mechatronic system which controls the auxiliary energy of a pneumatic actuating drive corresponding to one or more input signals, in order to move a valve element to a specific position. For operation, the position regulation may be supplied with pressurized gas, such as compressed air, as auxiliary energy, as well as electrical energy.
A known pneumatic position regulator includes several components referred to in more detail below. The drive chambers of a single-acting or double-acting pneumatic actuating drive are deliberately ventilated or vented as a function of one or more input signals, by means of a pneumatic system. The pneumatic system includes an auxiliary energy supply line, one or more pilot valve arrangements, and control pressure supply lines to the drive chambers in order to control the ventilation and/or venting of the drive chambers. The movements and positions of the valve element are represented as one or more signals, with the aid of a position sensor as a position feedback sensor system. Furthermore, control electronics are provided. The control electronics have a microcontroller and receive one or more input signals. The firmware in the control electronics processes the input signals and the signals in the position sensor to form output signals, which are used as input signals for the pneumatic system.
Actuating drives of the type of interest here are subdivided into pivoting drives and linear-movement drives. In the case of a linear-movement drive, the linear movement of the output drive of the actuating drive is transmitted directly to a linearly operated actuating member. On the other hand, in the case of the pivoting drive, the linear movement of the output drive of the actuating drive is converted to a rotary movement, by suitable conversion means.
The pneumatic actuating drive and the position regulation are connected by means of a fitting kit. The fitting kit comprises components which transmit the movement and position of the actuating drive with respect to the position feedback sensor system to the position regulation.
One issue when using valve arrangements such as this for installation control purposes is that, in the event of an unpredicted failure of a pneumatic actuating drive, the entire installation may also fail, which leads to production down times. Multiway valves for switching of compressed-air flows are particularly susceptible to failure in a pneumatic secondary drive since they are normally subject to a particularly severe mechanical alternating load during operation.
In order to cope with this problem, it has been normal practice until now to carry out preventative replacement after an estimated valve life has elapsed. With this technique, the replacement was often carried out well before the actual wear limit, since there is often a wide variation range between the estimated life and the actual life.
In addition to this failure problem, it is also possible for progressive wear in an installation to result in the switching of the actuating drive taking place continuously more slowly, which can result in disadvantageous overlapping phenomena, which can in turn lead to impermissible system states in the installation.
DE 102 22 890 A1 discloses a technical solution which is appropriate for the problem as described above and proposes specific electronic monitoring means for wear state monitoring of a pneumatic valve. An electronics unit is provided for this purpose which, on the input side, receives the electrical drive signal which is predetermined by a central control unit for the pneumatic valve, and an electrical reaction signal which follows a drive pulse initiated thereby. The electronics unit compares the time interval between the drive signal and the reaction signal of the switching delay as a measure of the wear state of the valve mechanism. The reaction signal is in this case determined by means of a pressure sensor which is integrated on the operating line side in the valve housing. This solution is based on the knowledge that lengthening of the switching time of a valve is directly related to the wear state over its entire operating time. This known solution therefore makes use of timely identification of undesirably long switching times to allow deliberate replacement of pneumatic valves or their parts that are subject to wear and which would fail in the foreseeable future. This ensures preventative maintenance of pneumatic installations.
However, this technical solution appears to have the disadvantage of the pressure sensor system which is provided for the purpose of determining the reaction signal to an electrical drive pulse. This is because correct operation of a pressure sensor cannot be ensured in all circumstances over the entire life of the valve. Furthermore, pressure sensors result in consumption of additional electrical energy, and are not required during normal operation of the valve.
In addition, the solution described above is also disadvantageous because the friction which indicates the wear state of the valve mechanism does not remain constant over the entire switching travel. The friction may vary considerably over the switching travel, particularly in the case of a slide-type valve, for example. Variations such as these cannot be detected with sufficiently high resolution by a pressure sensor system. Particularly if the valve element has to move over a relatively long switching travel, the friction as an indication of the wear state changes at a large number of switching positions. The friction along the switching travel is highly dependent on the internal diameter of the bore which guides the valve element, and on the component tolerances. This phenomenon is likewise included in the position-dependent wear state. Friction measurements or determinations which consider only the friction at a small number of position points along the switching travel will accordingly not reflect the correct wear state.